The embodiments herein relate generally to devices for determining the gases present in an air sample or breath sample.
The human breath is complex and is estimated to have as many as 200 different gas components in a typical sample. Some of these gases are present in small quantities such as 1-100 parts per billion (ppb), which presents a need for accurate methods and devices to properly detect these components.
Several techniques available in the field such as chemo-resistive analyses are used to determine the ratio of gases present in a sample. During these analyses, gases in a sample interact with sensors, which causes the resistance properties of the sensors to change. The sensing material of the chemo-sensors are generally heated to a high temperature within the range of 50-700 degrees Celsius. This heating process increases the selectivity and sensitivity of the chemo-sensors to the present gases at certain temperatures. By measuring the resistances of one or more chemo-sensors at various temperatures, the ratio of gases present in a sample can be estimated. Therefore, it is critical when performing chemo-resistive analyses to heat each sensor to a particular temperature by using a microheater element.
The development of microheaters (microhotplates) as platforms for microsensors has been widely reported for gas sensing applications. However, the cost and design of the microheaters is challenging, particularly for portable and disposable gas sensing applications. For example, the serpentine polysilicon heater or other conductive materials must be embedded within two electrically insulating members (e.g. SiO2 layers) several micrometers in thickness. Further, fabricating a low power sensor with rapid heating or cooling characteristics with a surface that is easy to clean poses many challenges. Current microheaters have these limitations and require external power sources such as batteries or power outlets to operate. This limits the practicality of the devices and places several burdens on the operator.
As such, there is the need for a low power gas-sensing apparatus with reduced power requirements that addresses the limitations of the prior art, which includes a self-powered microheater.